Dunes travel across deserts like waves across a sea—writhing, rippling, and rolling.
Winds are one driver of their sinuous creep, sculpting them into towering pyramids or low-lying ridges that slowly migrate across the landscape.
Now, two scientists at King’s College London are investigating how wind patterns shifting as a result of climate change could remodel dunes around the world. Their preliminary research suggests that dunes in the tropics and equatorial regions could migrate more by the end of the century.
“There are plenty of documented cases where sand dunes have migrated over agricultural fields,” said Andreas Baas, an aeolian geomorphologist at King’s College London. Considering this research, he added, communities may want to adjust how they bulldoze sand and plan their cities in the future.
By the end of the century, several key sand seas in the northern Sahara could experience increased sand drift potential, the likelihood that sand will move if no vegetation holds it down and nothing stands in its way. Parts of Australia, too, will see higher sand drift in certain directions by 2100.
Conversely, sand drift potential for dunes in the North American Great Plains region will drop by 2100 using the same model.
The wind projections come from a popular climate model, CMIP6 (Coupled Model Intercomparison Project Phase 6), that was used in the latest U.N. report on climate impacts released this year. The simulation from the latest study assumes that humans will not curb greenhouse gas emissions, rocketing global temperatures 5°C above average by the end of the century.
Two Examples in the Desert
Baas pointed to two specific locations of change.
In Australia’s Great Victoria Desert, new winds could breathe life into dormant dunes. Historically, the winds in the area come from multiple directions, causing linear-shaped dunes. These dunes are now covered in vegetation and don’t move.
But climate change could alter the wind so that it arrives from just one direction, which would cause crescent-shaped barchan dunes to form. Soil moisture deficit projections suggest that a drought in the region might make it easier for the dunes to mobilize as vegetation dies out, said Baas.
In the other hemisphere, agricultural fields in southern Egypt could be at risk if climate change forces the wind to shift. A series of barchan dunes that are migrating southward could turn eastward toward irrigated fields, the analysis finds. The winds there will rotate by nearly 90° counterclockwise by the end of the century.
The small dunes in the area could “turn” relatively quickly, said Baas.
Andrew Gunn, a geomorphologist at Stanford University, dedicated his recently finished doctoral dissertation to this question. Gunn said that he sees consistency across his model and that of Baas. He found that overall, dune activity reduces with climate change.
The projections are still preliminary and have not been peer reviewed. Baas will present the work on 17 December at AGU’s Fall Meeting.
Downwind from Climate Change
Dunes will change shape because of the winds, but what’s modifying the winds?
In the most basic sense, the temperature difference between the poles and the equator determines the global air circulation. As the poles warm, the circulation between the polar regions and the equator weakens. At the same time, warmer air in the atmosphere gives it more energy, strengthening winds from other directions.
But making such overarching projections can be tricky. “Wind field predictions tend to have higher uncertainty than other key climate variables,” said Gunn, who did not participate in the work.
Next, Baas plans to study how soil moisture and vegetation might influence how dunes respond to shifting winds.
“There is a lot of attention in climate change research on the water side of things and those impacts, but not so much on deserts and arid land zones,” Baas said.
That grabbed his attention: “It seemed to be an open gap in climate change research.”
—Jenessa Duncombe (@jrdscience), Staff Writer